Matrix-stiffened alloy



United States Patent C) 3,160,500 MA'lRlX-STIFFENED ALLOY Herbert Louis Eiselstein and John Gadbut, Huntington,

W. Va., assignors to The international Nickel Company, Inc, New York, N.Y., a corporation of Delaware No Drawing. Filed Jan. 24, 1962, Ser. No. 168,512 2 Claims. (Cl. 75-171) The present invention relates to a matrix-stiffened nickel-chromium alloy and, more particularly, to such a matrix-stiffened alloy having a high combination of mechanical properties over a wide range of temperature and having high resistance to rupture and stress at elevated temperature.

It is well'known that alloys which are required to withstand the combined effects of stress and elevated temperature over extended periods of time should have a stable microstructure which does not suffer decomposition and/ or other destructive effects as a result of the prolonged exposure to stress at elevated temperature. It is also well known that alloys required for such service should be free from weld cracking resulting from post Weld heat treatments. The art has endeavored to provide alloys for service under the Boiler Code but up to the present time the alloys available for such service are greatly restricted in properties and are generally unsatisfactory from the standpoint of the designer. Thus, it is known that, under the Boiler Code, alloys for service at elevated temperatures up to about 1500 F. should have a high yield strength, a high tensile strength, together with'high creep strength, and high rupture strength in the softened and annealed condition. Furthermore, it is preferred that such alloys be essentially non-age hardenable. Although many attempts were made to overcome the foregoing difficulties and other 'ditficulties, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that a nickel-chromium base alloy containing a special combination of ingredients in limited ranges provides an enhanced combination of properties not only at room temperature but at elevated temperatures up to about 1500 F. and freedom from weld cracking.

It is an object of the present invention to provide a nickel-chromium alloy particularly adapted for service under applications covered by the Boiler Code.

Another object of the invention is to provide a matrixstitfened nickel-chromium alloy having a high combination of properties at room temperature and at elevated temperatures up to about 1500 F.

The invention also contemplates providing a matrixstilfened nickel-chromium base alloy which is readily weldable and which is free from weld cracking.

Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention relates to a matrix-stiffened nickel-base alloy having high strength at temperatures up to about 1500 F. comprising about 55% to 62% nickel, about 7% to 11% molybdenum, about 3% to 4.5% columbium, about to 24% chromium, up to about 8% tungsten, not more than about 0.1% carbon, e.g., up to about 0.05% carbon, up to about 0.5% silicon, up to about 0.5 manganese, up to about 0.015% boron, not more than 0.4% of deoxidizing elements from the group consisting of aluminum and 3,150,500 Patented Dec. 8, 1964 room temperature yield strength (0.2% set) of at least about 60,000 psi. and by a rupture life at 1200 F. and 70,000 p.s.i. of at least about hours. A particularly advantageous composition contemplated in accordance" with the invention contains about 60% nickel, about 22% chromium, about 9% molybdenum, about4% columbium, about 0.2% aluminum, about 0.15% titanium, about 0.03% carbon and the balance essentially iron. 7

Alloys within the invention are essentially non-age hardenable, i.e., the alloys will not increase in yield strength more than about 20,000 pounds per square inch when subjected to a heat treatment at temperatures in the range of about 1100 F. to 1300 F. as compared to the yield strength developed in the annealed condition. In addition, alloys within the invention will withstand prolonged exposure to loads at high temperatures without any appreciable loss in load-carrying ability.

Nickel in the alloys provided in accordance with the invention is very important and is maintained within the range of about 55% to 62% in order to impart rupture .strength to the alloy. Columbium also plays a very important role in contributing rupture strength and room temperature yield strength to the alloy. 4 Chromium and molybdenum also contribute importantly to the strength of the alloy and, in combination with the other necessary ingredients therein, provide the high tensile properties which characterize the special alloy provided in accordance with the invention. chromium content of the alloy, the more molybdenum should be used to insure that high tensile properties will be obtained. When tungsten is present in the alloy, it

contributes to the room-temperature strength and to the rupture strength of'the alloy.

' It is important that alloys produced in accordance with the invention be thoroughly deoxidized. Usual deoxidation procedures known to those skilled in the art may be.

employed in producing the alloys but it is advantageous to employ a combination of aluminum and titanium for deoxidation purposes. When these metals are employed to deoxidize the alloys, at least about 0.02% of aluminum columbium content, should not exceed about 0.4% as otherwise the alloys tend to become age hardenable. Boron in amounts of about 0.005% and up to about 0.015%, may be employed in the alloy although boron appears to reduce the hot malleability of the alloy. It

appears that magnesium in residual amounts of about 0.02% to about 0.05% contributes in an important manner to development of hot malleability in the alloys provided in accordance with the invention. Alloys produced in accordance with the invention'advantageously have a low carbon content not exceeding about 0.1% carbon. The alloys may also contain silicon up to about 0.5%, e.g., about 0.1% to about 0.5%, and manganese up to about 0.5%, e.g., about 0.1% to about 0.5%. It is important that the silicon and manganese contents of the alloys not exceed the foregoing maxima as otherwise the high temperature strength of the alloys is detrimentally affected. Other minor elements and impurities suchas sulfur, copper, phosphorus (0.025% maximum) and V In general, the lower the' nitrogen (0.03% maximum) may be present in the aggregate in amounts of up to about 0.1% without detriment to mechanical properties or malleability. It is irnportant that the sulfur content be below 0.02%. Copperv may be present in the alloysin an amount up to about 0.1%, e.g., about 0.01% to about 0.1%.

In order to give those skilled in the art a better understanding of the invention, the compositions of alloys contemplated in accordance with the invention are set forth *Alloy 2 also contained 5.32% tungsten;

Norm-The alloys in Table I also contained about 0.003% to 0.009% sulfur, about 0.03% copper and about.0.025% magnesium resulting from an addition of about'0.05% magnesium to the respective melts.

Metal taken from melts of the foregoing alloys was forged to provide about 98% reduction from the ingot form and the forgings were annealed at 1900 F. for one hour. The tensile properties thereof at room temperature were determinedwith the resultsset forth in the following Table II:

Table II Yield Tensile Reduction Alloy No. strength, strength, Elong., in area, p.s.i. (0.2% p.s.i. percent percent set) It is to be noted that the properties given in Table II were obtained on annealed alloys. It will be'understood that much higher tensile properties are developed in alloys of the invention in the as-forged condition attendant upon the hot-cold working effect of forging.

Stress-rupture tests were conducted on the forged, annealed (1900 F. for one hour) metal with the results set forth in the following Table III:

Table III Test Conditions Reduc- Life, Elong., tien in Alloy No. Hours percent area,

Temp, Stress, percent F. p.s.i.

From the foregoing, it is to be seen that alloys within the invention have: high stress-rupture life.

Thus, alloy No. lexliibited a l-hour stress-rupture life at 1400 F. in the annealed condition at a stress of about 23,000 p.s.i., whereas a 26% chromium-20% nickel casting alloy presently employed in elevatedtemperature service exhibited reductionin area of 68% when tested after a 1900 F..

4 cordance with the invention, an alloy outside the invention and containing 50.8% nickel, 21.76% chromium, 9.07% molybdenum, 4.37% columbium and the balance essentially iron was produced. In the annealed condition, this alloy had a room temperature yield strength of 66,500 pounds per square inch. However, when subjected to a rupture test at 1200 F. and 70,000 pounds per square inch, the alloy had a life of only '33 hours. On the other hand, as pointed out hereinbefore, alloy No. 1, which contained about 57% nickel and was otherwise similar in composition, had the much higher rupture life of 206 hours under the same conditions. As a further demonstration of the disadvantageous properties encountered in alloys outside the invention, an alloy outside the invention containing 0.04% carbon, 0.15% manganese, 17.1% iron, 21.4% chromium, 0.6% aluminum, 0.67% titanium, 1.2% columbium, 5.1% molybdenum, and the balance essentially nickel was produced. This alloy age hardened strongly but had a-yield strength at room temperature of only 49,500 p.s.i., together with. a tensile strength of 113,000 p.s.i., an elongation of 47%. and a anneal. When subjected to a stress-rupture-test in the annealed and aged condition (1900 F. for one hour followed by a water quench and an. aging treatment of 1250 F. for 16 hours)v the alloy provided a life to-rup-' ture of only 64.1 hours with an elongation of 16% under Aswill be test conditions of 1200 F. and 70,000 p.s.i. seen from other data presented hereinbefore, the essentiallynon-age hardenable alloys'withinthe invention are stronger in the annealed condition than this age-hardenable alloy outside the invention.

While the properties given hereinbefore for alloys It is to be understood that when the term columbium is used herein, pure columbium and columbium containing tantalum in the amount of up to about 'by weight of the columbium are'included, since,- as those skilled in the art know, commercial grades of columbiurnusually contain a small proportion of tantalum.

Alloys provided in accordance with the invention may be welded by conventional means such as arc welding techniques (including inert-gas, shielded-arc welding with either a tungsten electrode or a consumable electrode), the gas welding technique, etc. in the alloy provided in accordance with the invention need not be annealed after welding to restore mechanical properties, to avoid impairment of corrosion resistance in the heat-affected areas, etc. The alloys are readily wrought using conventional'techniques such as forging, rolling, extrusion, etc., and may bev provided in any of the usual mill forms, including sheet, rod, tubing, strip, etc. The alloys described herein are particularly useful in the form of heavy weldable forgings such as those employed in steam plant service. Because of the high oxidation and corrosion resistance of the alloy, parts madev thereof are very useful in heat treating furnaces, as con veyor belts, rolls, heat treating boXesand baskets and in various forms required in ethylene furnaces, hydrogen reforming furnaces and the like. Thealloys are also very useful when fabricated into forms such. as sandwich sheet structures, weldments exposed to stress at' elevated temperatures, airframe components, aircraft and jet engine parts including tail pipes, last stage compressor blading and the like, springs, machine components for cryogenie uses, etc. 7

Although the present invention has been described in conjunction with preferred embodiments, it is to be under- Weldments produced r V 5 stood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A nickel-base alloy containing about 21.44% to 21.68% chromium, about 0.02% to 0.03% carbon, about 0.11% to 0.12% manganese,about 0.04% to 0.11% silicon, about 8.83% to 9.10% molybdenum, up to 5.32%

tungsten, about 4.19% to 4.30% columbium, deoxidizing amounts of aluminum. and titanium consisting of about 0.16% to 0.23% aluminum and about 0.13% to 0.20% titanium, with the total content of aluminum and titanium not exceeding 0.38%, about 1.92% to about 6.89% iron, about 0.02% magnesium and the balance essentially nickel, said alloy being characterized by the ability to withstand prolonged exposure to load at high temperatures without any appreciable loss in load-carrying ability and ductility, by a yield strength (0.2% ofrset) at room temperature of at least about 73,000 pounds per square inch in the annealed condition and by a life to rupture of at least about 200 hours at 1200 F. and 70,000

pounds per square inch in the annealed condition together with an elongation of at least about 14% under these stress-rupture test conditions, and being further characterized in that the yield strength'of the annealed alloy does not increase more than about 20,000 p.s.i. when subjected to an aging heat treatment. 7

2. A nickel-base alloy characterized in the annealed condition by high yield strength at room temperature and by high rupture strength at elevated temperatures which consists essentially of about, 60% nickel, about 22% chromium, about 9% molybdenum, about 3% to about 4.5% columbium, deoxidizing amounts of aluminum and titanium consisting of about 0.2% aluminum and about 0.15% titanium, about 0.03% carbon, and the balance essentially iron.

ReEerences Cited in the file of this patent UNITED STATES PATENTS Great Britain Sept. 2, 1948 

1. A NICKEL-BASE ALLOY CONTAINING ABOUT 21.44% TO 21.68% CHROMIUM, ABOUT 0.02% TO 0.03% CARBON, ABOUT 0.11% TO 0.12% MANGANESE, ABOUT 0.04% TO 0.11% SILICON, ABOUT 8.83% TO 9.10% MOLYBDENUM, UP TO 5.32% TUNGSTEN, ABOUT 4.19% TO 4.30% COLUMBIUM, DEOXIDIZING AMOUNTS OF ALUMINUM AND TITANIUM CONSISTING OF AOBUT 0.16% TO 0.23% ALUMINUM AND ABOUT 0.13% TO 0.20% TITANIUM, WITH THE TOTAL CONTENT OF ALUMINUM AND TITANIUM NOT EXCEEDING 0.38%, ABOUT 1.92% TO ABOUT 6.89% IRON, ABOUT 0.02% MAGNESIUM AND THE BALANCE ESSENTIALLY NICKEL, SAID ALLOY BEING CHARACTERIZED BY THE ABILITY TO WITHSTAND PROLONGED EXPOSURE TO LOAD AT HIGH TEMPERATURES WITHOUT ANY APPRECIABLE LOSS IN LOAD-CARRYING ABILITY AND DUCTILITY, BY A YIELD STRENGTH (0.2% OFFSET) AT ROOM TEMPERATURE OF AT LEAST ABOUT 73,000 POUNDS PER SQUARE INCH IN THE ANNEALSED CONDITION AND BY A LIFE TO RUPTURE OF AT LEAST ABOUT 200 HOURS AT 1200*F. AND 70,000 POUNDS PER SQUARE INCH IN THE ANNEALED CONDITION TOGETHER WITH AN ELONGATION OF AT LEAST ABOUT 14% UNDER THESE STRESS-RUPTURE TEST CONDIDITONS, AND BEING FURTHER CHARACTERIZED IN THAT THE YIELD STRENGTH OF THE ANNEALED ALLOY DOES NOT INCREASE MORE THAN AOBUT 20,000 P.S.I. WHEN SUBJECTED TO AN AGING HEAT TREATMENT. 